Semiconductor laser device and wire bonding method capable of easily performing reliable wire bonding

ABSTRACT

There is provided is a semiconductor laser device capable of simplifying fabricating processes with a simple construction and easily mounting two semiconductor laser elements and a monitoring PD on a compact package and a wire bonding method for the semiconductor laser device. There are provided a stem  100  provided with a plurality of lead pins  121  through  124 , a sub-mount  160  that is die-bonded onto the stem  100  and has its surface formed integrally with a monitoring PD  140  and two semiconductor laser elements  131  and  132  that are die-bonded onto the sub-mount  160  and have emission light monitored by the monitoring PD  140 . A first bonding surface i.e. anode electrode  183  of the monitoring PD  140  and a second bonding surface i.e. end surface  123   a  of a lead pin  123  that is approximately perpendicular to the first bonding surface are wire-bonded to each other.

This application is a division of application Ser. No. 09/803,658 filedMar. 12, 2001, now U.S. Pat. No. 6,562,693 the entire content of whichis hereby incorporated by reference in this application.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor laser device includingtwo semiconductor laser elements and a wire bonding method for thedevice.

Conventionally, there has been a semiconductor laser device in which onesemiconductor laser element and a monitoring use photodiode (hereinafterreferred to as a monitoring PD) for monitoring an output of thesemiconductor laser element are arranged on a metallic stem. However, inorder to read information from a recorded medium such as a CD (compactdisc) and a DVD (digital versatile disk), there is needed asemiconductor laser device that emits two kinds of laser light ofdifferent wave lengths by means of two semiconductor laser elements.

Accordingly, there can be considered a semiconductor laser device asshown in FIG. 12 where two semiconductor laser elements and a monitoringPD for monitoring the output of the semiconductor laser element arearranged. FIG. 12 shows a perspective view of the inside of thissemiconductor laser device with its cap removed. It is to be noted thatthis semiconductor laser device is shown for facilitating theexplanation of this invention and is not the prior art.

As shown in FIG. 12, this semiconductor laser device includes a metallicstem 200 having an eyelet 201 and a heat radiation base 202 which areintegrally formed. Lead pins 221 through 223 are mounted on the eyelet201 of the stem 200 so that one end penetrates the eyelet 201 of thestem 200, and one end of a lead pin 224 is electrically connected as acommon electrode to the eyelet 201. The lead pins 221 through 223 arefixed to the eyelet 201 with a low melting point glass and electricallyinsulated with respect to the stem 200. The eyelet 201 has an outerdiameter of 5.6 mm, and the lead pins 221 through 224 constructed of acolumnar metal having a diameter of 0.4 mm are arranged at regularintervals of 90 degrees in a circle of a diameter of 2 mm.

A silicon sub-mount (hereinafter referred to as an Si sub-mount) 260 isdie-bonded to the heat radiation base 202 formed integrally with theeyelet 201 with a conductive paste (not shown). Two semiconductor laserelements 231 and 232 are die-bonded onto the silicon sub-mount 260 witha brazing material (not shown) made of an Au—Sn alloy. The die bondingsurface of the Si sub-mount 260 is covered with a metal, providing acommon electrode of the semiconductor laser elements 231 and 232. Thecommon electrode on the surface of the Si sub-mount 260 is connected tothe heat radiation base 202 via metal wires 252 and 254, respectively.On the other hand, upper electrodes of the semiconductor laser elements231 and 232 are connected to the lead pins 221 and 222 via metal wires251 and 253, respectively. A monitoring PD 240 is die-bonded to a recess201 b formed on the eyelet 201 of the stem 200 with a conductive paste(not shown), and an upper electrode of the monitoring PD 240 isconnected to an end surface 223 a of the lead pin 223 via a metal wire255.

The two semiconductor laser elements 231 and 232 are providedparticularly by a combination of an InGaAlP based semiconductor laserelement 231 that emits red laser light (having a wavelength of 630 nm to680 nm) and an AlGaAs based semiconductor laser element 232 that emitsinfrared laser light (having a wavelength of 760 nm to 850 nm).

It is required to die-bond the semiconductor laser elements 231 and 232onto the Si sub-mount 260 by using a brazing material (Au—Sn alloy, forexample) whose melting point is sufficiently higher than a temperatureof 80° C., which is the upper limit of the normal use temperature rangeso as not to move the relative positions of the light emitting points ofthe two semiconductor laser elements 231 and 232 in operation. If thesemiconductor laser elements 231 and 232 are die-bonded directly to themetallic heat radiation base 202, then there is the problem that anintense stress is applied to the semiconductor laser elements 231 and232 due to a difference in the linear expansion coefficient of the metaland the semiconductor, consequently destroying and deteriorating thecrystal. Therefore, it is indispensable to perform the die bonding tothe Si sub-mount 260.

The semiconductor laser device having two semiconductor laser elementsshown in FIG. 12 has the problem of complicated structure, and theprocesses of die-bonding the monitoring PD 240 and the Si sub-mount 260increase cost.

Accordingly, it can be considered to simplify the fabricating processesby forming a monitoring PD on the surface of the Si sub-mount andeliminating the die bonding process of the monitoring PD. If theabove-mentioned structure is adopted, then the electrode surface of themonitoring PD becomes parallel to the electrode surfaces of the twosemiconductor laser elements and the electrode surface formed on thesurface of the Si sub-mount. The wire bonding cannot easily be performedunless the surfaces of the electrodes of the semiconductor laserelements and the monitoring PD and the surfaces of the lead pins towhich metal wires are to be bonded are parallel to one another whenconnecting the electrodes of these semiconductor laser elements and themonitoring PD with the lead pins by way of metal wires. This will bedescribed below on the basis of the semiconductor laser device of theconstruction shown in FIG. 12 (monitoring PD is assumed to be formed onthe surface of the Si sub-mount).

In this semiconductor laser device, the two semiconductor laser elements231 and 232 are connected to the lead pins 221 and 222, respectively,located on both sides. Accordingly, there is only the lead pin 223 thatis located on the upper side in FIG. 12 and is able to be connected tothe electrode of the monitoring PD formed on the surface of the Sisub-mount. In this case, there is the problem that almost no surfaceparallel to the electrode of the monitoring PD to be formed on the Sisub-mount 260 exists since the tip of the lead pin 223 is not protrudingfrom a surface 201a of the eyelet 201. As a method for solving thisproblem, it can also be considered to provide a recess around the leadpin 223 on the eyelet 201 to expose the lead pin 223 and performdie-bonding to the outer peripheral surface of the cylindrical lead pin223. However, such a recess may penetrate the eyelet 201 to disable thesealing of the inside with a cap (not shown), which would cause aproblem that the semiconductor laser elements easily deteriorate.

When wire-bonding the end surface 223 a of the lead pin 223 to theelectrode of the monitoring PD formed on the Si sub-mount 260, the endsurface 223 a of the lead pin 223 and the electrode surface of themonitoring PD are perpendicular to each other, and therefore, it hasbeen difficult to connect the surfaces together by the conventional wirebonding method. The reason for the above will be described below withreference to FIG. 13 through FIG. 19, which show the wire bondingprocesses of the semiconductor laser device of FIG. 12.

First of all, the wire bonding method for connecting the electrodesurface of the monitoring PD 240 of the semiconductor laser device 200shown in FIG. 12 with the end surface 223 a of the lead pin 223 by wayof a metal wire will be described with reference to FIG. 13 through FIG.18.

As shown in FIG. 13, a bonding head 70 has a capillary 71 attached tothe tip of a capillary holder 72 and a wire clamp 73, and the capillary71 and the wire clamp 73 move in such a manner as an integrated body.The capillary 71 has a tip diameter of about 200 μm and operates toguide a metal wire 50 kept linear. A gold wire having a diameter of 25μm is used as this metal wire 50, and a ball 50 a is formed by arcdischarge or the like at the tip of the metal wire 50 that protrudesfrom the tip of the capillary 71.

Next, the bonding head 70 is moved down as shown in FIG. 14 to bring theball 50 a (shown in FIG. 13) in contact with the electrode surface ofthe monitoring PD 240, and supersonic vibrations are applied to the ball50 a to connect the ball 50 a to the electrode of the monitoring PD 240(the point to which this ball 50 a is connected is referred to as a“first bond”).

Next, the bonding head 70 is moved up with the wire clamp 73 opened asshown in FIG. 15 to draw the metal wire 50, while the stem 200 isproperly turned around an axis perpendicular to the axial direction ofthe capillary 71 to set the bonding surface 223 a of the lead pin 223perpendicular to the axial direction of the capillary 71.

Next, as shown in FIG. 16, the bonding head 70 is moved along a planeparallel to the bonding surface 223 a of the lead pin 223 so as tolocate the bonding surface 223 a of the lead pin 223 perpendicularlybelow the capillary 71. If the electrode surface of the monitoring PD240 and the bonding surface 223 a of the lead pin 223 are not located inan identical plane with respect to the metal wire 50 guided by thecapillary 71 in this stage, then it is proper to move the stem 200 sothat the bonding surface 223 a of the lead pin 223 is located on theaxis of the capillary 71.

As shown in FIG. 17, the bonding head 70 is moved down again to bringthe metal wire 50 in contact with the bonding surface 223 a of the leadpin 223, and supersonic vibrations are applied to the metal wire 50 toconnect the metal wire 50 to the bonding surface 223 a of the lead pin223 (the point to which this metal wire is connected is referred to as a“second bond”).

Finally, as shown in FIG. 18, the metal wire 50 is cut by closing thewire clamp 73 and moving up the bonding head 70 in this state.Subsequently, a metal ball is formed at the tip of the wire 50 by arcdischarge although not shown, and the process flow returns to the firstprocess.

According to the aforementioned wire bonding method, there is noparticular problem wherever the axis of the center of turn of the stem200 exists since the bonding surface of the first bond and the bondingsurface of the second bond make an angle of about 13° between them.However, there is the problem that, if the angle of turn of the stem 200is further increased, then the capillary 71 might be damaged by beingbrought in contact with the stem 200, the semiconductor laser element orthe like, and as shown in FIG. 19, this leads to the problem that themetal wire 50 might be significantly bent at the tip of the capillary 71or distorted and cut in the portions of the first bond and the tip ofthe capillary 71.

When die-bonding the Si sub-mount 260 to the heat radiation base 202 inthe semiconductor laser device shown in FIG. 12, it is desirable to fixthem with a conductive paste obtained by filling a resin with aconductive material (silver filler, for example) so as not to exert athermal influence on the brazing material that fixes the semiconductorlaser elements 231 and 232 to the Si sub-mount 260. However, there isthe problem that the wire bonding cannot be performed when smoothness islost due to the conductive paste adhering to the surface to which themetal wire is to be bonded, since the conductive paste has highliquidity and tends to spread over the die-bonding surface.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide asemiconductor laser device capable of simplifying the fabricatingprocesses with a simple construction and easily mounting twosemiconductor laser elements and a monitoring PD on a compact packageand a wire bonding method for the above-mentioned semiconductor laserdevice capable of easily performing reliable wire bonding withoutdamaging a stem, the semiconductor laser elements and so on.

In order to achieve the aforementioned object, the present inventionprovides a semiconductor laser device comprising:

a stem provided with a plurality of lead pins;

a sub-mount that is die-bonded onto the stem and has a surface formedintegrally with a monitoring photodiode; and

two semiconductor laser elements that are die-bonded onto the sub-mountand have emission light monitored by the monitoring photodiode,

the semiconductor laser elements having electrodes electricallyconnected to the respective lead pins via metal wires and the monitoringphotodiode having an electrode electrically connected to thecorresponding lead pin via a metal wire, wherein

at least one first bonding surface of the two semiconductor laserelements and the monitoring photodiode is approximately perpendicular toa second bonding surface of the lead pin to be wire-bonded to the firstbonding surface.

According to the semiconductor laser device having the above-mentionedconstruction, the electrodes of the two semiconductor laser elements andthe electrode of the monitoring PD have mutually parallel electrodesurfaces, and at least one of those three electrode surfaces is made toserve as a first bonding surface, which is wire-bonded to the secondbonding surface of the lead pin approximately perpendicular to the firstbonding surface. For example, in a small-size package having a diameterof 5.6 mm with a limited number of lead pins, the two semiconductorlaser elements are arranged on the stem so that the optical axes of theemission light of the two semiconductor laser elements become parallelto each other and perpendicular to the stem surface (eyelet surface). Iftwo lead pins exist on both sides of the direction of arrangement andanother lead pin exists in a direction perpendicular to the direction ofarrangement, then the electrodes of the semiconductor laser elements andthe electrode of the monitoring PD are assigned to the three lead pins,and the electrodes and the lead pins are connected together by wirebonding (the other electrode of each element is connected to the stemthat serves as a common electrode). In the above case, tangent planes onthe peripheries of the lead pins on both sides of the direction ofarrangement of the two semiconductor laser elements and two electrodesurfaces out of the electrode of the semiconductor laser elements andthe electrode of the monitoring PD become parallel to each other,allowing the wire bonding to be easily performed. However, the electrodesurface (first bonding surface) of the remaining element, which is alsoparallel to a tangent plane on the periphery of the remaining lead pin,is wire-bonded to the end surface (second bonding surface) of the leadpin that is approximately perpendicular to the electrode surface (firstbonding surface) of the remaining element. By thus enabling the wirebonding of the first and second bonding surfaces that are approximatelyperpendicular to each other, the fabricating processes can be simplifiedwith a simple construction, and a semiconductor laser element capable ofeasily mounting the stem of a small-size package with two semiconductorlaser elements and a monitoring PD can be provided. It is to be notedthat a sub-mount to which the two semiconductor laser elements are to bedie-bonded is provided by a sub-mount made of a semiconductor such assilicon so that a stress due to thermal expansion will not be applied tothe semiconductor laser element.

In the semiconductor laser device of one embodiment, a bonding positionof the first bonding surface and a bonding position of the secondbonding surface are located in an identical plane approximatelyperpendicular to the first and second bonding surfaces.

According to the semiconductor laser device of the above embodiment, thebonding position of the first bonding surface and the bonding positionof the second bonding surface are located in the identical planeapproximately perpendicular to the first and second bonding surfaces.With this arrangement, the stem is turned along the identical plane inthe wire bonding stage. Therefore, the metal-wire is not twisted and nostress is applied to the semiconductor laser elements and the monitoringPD to which the metal wires are connected. Therefore, the reliabilitycan be improved.

The semiconductor laser device of one embodiment further comprises metallines, which are formed on the sub-mount and to which the twosemiconductor laser elements are respectively die-bonded, wherein

the metal lines corresponding to the semiconductor laser elements areelectrically insulated from each other.

According to the semiconductor laser device of the above embodiment, themetal lines, which are located on the sub-mount and to which thesemiconductor laser elements are die-bonded, are independent metal linesprovided for the respective semiconductor laser elements andelectrically insulated from each other. This arrangement allows the twosemiconductor laser elements to have different electricalcharacteristics on the die-bonding side. For example, it is acceptableto die-bond the p-electrode side of one semiconductor laser element anddie-bond the n-electrode side of the other semiconductor laser element.Therefore, the conditions of the semiconductor laser elements to beemployed have greater tolerance.

The semiconductor laser device of one embodiment further comprises metallines, which are formed on the sub-mount and to which the twosemiconductor laser elements are die-bonded, wherein

no metal line is formed from a rear end surface of at least one of thetwo semiconductor laser elements toward the monitoring photodiode.

According to the semiconductor laser device of the above embodiment, atleast one of the metal lines is prevented from protruding from thesemiconductor laser element toward the monitoring PD in the vicinity ofthe emission end surfaces of the semiconductor laser elements in orderto make the largest amount of emission light from the semiconductorlaser incident on the monitoring PD formed integrally with thesub-mount. This arrangement is effective particularly for thesemiconductor laser element whose light emitting point is locatedseveral micrometers higher than the surface of the sub-mount.

In the semiconductor laser device of one embodiment, an end surface ofthe lead pin is the second bonding surface, and

the end surface of the lead pin is located at a height equal to a heightof the surface of the stem or lower than the height of the surface ofthe stem.

According to the semiconductor laser device of the above embodiment, thecapillary of the wire bonding apparatus can be prevented from strikingagainst the lead pin that has the second bonding surface when performingwire bonding to the first bonding surface since the end surface of thelead pin, or the second bonding surface is located at the same height asthat of the surface of the stem or lower than the surface of the stem.

In the semiconductor laser device of one embodiment, the stem isprovided with stepped portions having bonding surfaces that are parallelto and different in height from a surface to which the sub-mount isbonded.

According to the semiconductor laser device of the above embodiment, thestem is provided with the stepped portions having the bonding surfacesthat are parallel to and different in height from the surface to whichthe sub-mount is bonded. This arrangement eliminates the possibility ofthe occurrence of the problem that the wire bonding cannot be performedsince the conductive paste on the stem surface to which the sub-mount isbonded does not adhere to the wire bonding surface.

The present invention also provides a semiconductor laser devicecomprising:

a stem provided with a plurality of lead pins;

a sub-mount die-bonded onto the stem; and

a semiconductor laser element die-bonded onto the sub-mount thesemiconductor laser element having an electrode electrically connectedto the lead pin via a metal wire, wherein

the stem is provided with stepped portions having bonding surfaces thatare parallel to and different in height from a surface to which thesub-mount is bonded.

According to the semiconductor laser device of the above embodiment, thestem is provided with the stepped portions having the bonding surfacesthat are parallel to and different in height from the surface to whichthe sub-mount is bonded. This arrangement eliminates the possibility ofthe occurrence of the problem that the wire bonding cannot be performedsince the conductive paste on the stem surface on which the sub-mount isbonded does not adhere to the wire bonding surface.

The present invention also provides a wire bonding method for asemiconductor laser device comprising a stem provided with a pluralityof lead pins; a sub-mount that is mounted on the stem and has a surfaceformed integrally with a monitoring photodiode; and two semiconductorlaser elements that are die-bonded onto the sub-mount and have emissionlight monitored by the monitoring photodiode, the method comprising:

a first step for retaining the stem so that an axis of a capillary forguiding a metal wire becomes perpendicular to at least one first bondingsurface of the two semiconductor laser elements and the monitoringphotodiode and bonding one end of the metal wire to the first bondingsurface; and

a second step for turning the stem so that the axis of the capillarybecomes perpendicular to a second bonding surface of the lead pinapproximately perpendicular to the first bonding surface around an axisperpendicular to the metal wire after performing bonding of one end ofthe metal wire to the first bonding surface and bonding the other end ofthe metal wire to the second bonding surface.

According to the above semiconductor laser device wire bonding method,the stem is retained so that the axis of the capillary of the wirebonding apparatus becomes perpendicular to at least one first bondingsurface of the two semiconductor laser elements and the monitoringphotodiode, and one end of the metal wire is bonded to the first bondingsurface. Thereafter, the stem is turned so that the axis of thecapillary becomes perpendicular to the second bonding surface of thelead pin approximately perpendicular to the first bonding surface aroundthe axis perpendicular to the metal wire, and the other end of the metalwire is bonded to the second bonding surface. Through these processes,the metal wire can be connected to the first and second bonding surfacesthat are about perpendicular to each other without twisting the metalwire to be bonded to the first and second bonding surfaces. Therefore, asemiconductor laser device capable of housing the two semiconductorlaser elements and the monitoring PD in a small-size package can easilybe subjected to wire bonding without damaging the stem, thesemiconductor laser elements and so on.

According to the semiconductor laser device wire bonding method of oneembodiment, the axis of turn of the stem in the second step is parallelto a line of intersection of the first and second bonding surfaces thatare approximately perpendicular to each other.

According to the semiconductor laser device wire bonding method of theabove embodiment, the axis of turn of the stem in the second step ismade parallel to the line of intersection of the first and secondbonding surfaces that are about perpendicular to each other, and thewire bonding is observed in the direction of the axis of turn of thestem. By this operation, the wire bonding can be performed whileobserving how the metal wire is twisted. Therefore, the bonding is notfailed, and the wire bonding can be reliably performed.

According to the semiconductor laser device wire bonding method of oneembodiment, a bonding position of the first bonding surface and abonding position of the second bonding surface are located in anidentical plane approximately perpendicular to the first and secondbonding surfaces.

According to the semiconductor laser device wire bonding method of theabove embodiment, the bonding position of the first bonding surface andthe bonding position of the second bonding surface are located in theidentical plane about perpendicular to the first and second bondingsurfaces, and the stem is turned along the identical surface in the wirebonding stage. Therefore, the metal wire is not twisted, and no stressis applied to the semiconductor laser element and the monitoring PD towhich the metal wires are connected. Therefore, the reliability can beimproved.

According to the semiconductor laser device wire bonding method of oneembodiment, a distance from the axis around which the stem is turned inthe second step to the first bonding surface is set equal to a distancefrom the axis around which the stem is turned to the second bondingsurface.

According to the semiconductor laser device wire bonding method of theabove embodiment, the distance from the axis around which the stem isturned to the first bonding surface is set equal to the distance fromthe axis to the second bonding surface. With this arrangement, thedistances- from the tip of the capillary to the first bonding surfaceand the second bonding surface becomes equal before and after the turn.Therefore, the wire bonding can easily be performed, and the bondedmetal wire is hard to come off.

According to the semiconductor laser device wire bonding method of oneembodiment, a length of the metal wire that is drawn out of a tip of thecapillary by pulling up the capillary in a direction perpendicular tothe first bonding surface after the first step is made longer than alength from a front end surface of the semiconductor laser element to abonding position of the first bonding surface.

According to the semiconductor laser device wire bonding method of theabove embodiment, the length of the metal wire to be drawn out of thetip of the capillary when the capillary is pulled up in the directionperpendicular to the first bonding surface after performing the bondingto the first bonding surface is made longer than the distance from thefront end surface of the semiconductor laser element to the bondingposition of the first bonding surface. With this arrangement, thecapillary can be prevented from striking against the semiconductor laserelement when the stem is turned.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a perspective view of a semiconductor laser device having twosemiconductor laser elements according to an embodiment of the presentinvention;

FIG. 2 is a front view of the essential part of the above semiconductorlaser device;

FIG. 3 is a top view of the essential part of the above semiconductorlaser device;

FIG. 4 is a view showing a bonding process of a 90°-wire of the abovesemiconductor laser device;

FIG. 5 is a view showing a bonding process subsequent to that of FIG. 4;

FIG. 6 is a view showing a bonding process subsequent to that of FIG. 5;

FIG. 7 is a view showing a bonding process subsequent to that of FIG. 6;

FIG. 8 is a view showing a bonding process subsequent to that of FIG. 7;

FIG. 9 is a view showing a bonding process subsequent to that of FIG. 8;

FIG. 10 is a view showing a bonding process subsequent to that of FIG.9;

FIG. 11 is a view showing a bonding process subsequent to that of FIG.10;

FIG. 12 is a perspective view of a semiconductor laser device having twosemiconductor laser elements;

FIG. 13 is a view showing a bonding process of a metal wire of the abovesemiconductor laser device;

FIG. 14 is a view showing a bonding process subsequent to that of FIG.13;

FIG. 15 is a view showing a bonding process subsequent to that of FIG.14;

FIG. 16 is a view showing a bonding process subsequent to that of FIG.15;

FIG. 17 is a view showing a bonding process subsequent to that of FIG.16;

FIG. 18 is a view showing a bonding process subsequent to that of FIG.17; and

FIG. 19 is an explanatory view showing the case where a stem is turnedby an angle of 90° in a metal wire bonding process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The semiconductor laser device and the wire bonding method of thepresent invention will be described in detail below on the basis of theembodiments thereof shown in the drawings.

FIG. 1 is a perspective view showing the inside of a semiconductor laserdevice according to an embodiment of the present invention, with its capremoved.

As shown in FIG. 1, this semiconductor laser device comprises a metallicstem 100 having an eyelet 101 and a heat radiation base 102, which areformed integrally. Lead pins 121 through 123 are mounted in the eyelet101 of the stem 100 so that ends of the lead pins 121 through 123penetrate the eyelet 101 of the stem 100, and one end of the lead pin124 used as a common electrode is electrically connected to the eyelet101. The lead pins 121 through 123 are fixed to the eyelet 101 with alow melting point glass and electrically insulated with respect to thestem 100. The eyelet 101 has an outer diameter of 5.6 mm, and the leadpins 121 through 124 having a cylindrical shape of a diameter of 0.4 mmand made of metal are arranged at regular intervals of 90 degrees in acircle of a diameter of 2 mm on the eyelet 101.

An Si sub-mount 160 is die-bonded to the heat radiation base 102 formedintegrally with the eyelet 101 with silver paste 170 (shown in FIG. 2)that is a conductive paste. A monitoring PD 140 is formed integrallywith the surface of this Si sub-mount 160. Further, two semiconductorlaser elements 131 and 132 are die-bonded onto the Si sub-mount 160 witha brazing material (not shown) made of an Au—Sn alloy. As shown in FIG.2, an upper electrode of the semiconductor laser element 131 isconnected to a surface 102 b of a stepped portion 111 of the heatradiation base 102 via a metal wire 152, and an upper electrode of thesemiconductor laser element 132 is connected to the lead pin 122 via ametal wire 153. On the other hand, a metal line 181 (shown in FIG. 3) onthe surface of the Si sub-mount 160 is connected to the lead pin 121 viaa metal wire 151, and a metal line 182 (shown in FIG. 3) on the surfaceof the Si sub-mount 160 is connected to a surface 102 b of the steppedportion 111 of the heat radiation base 102 via a metal wire 154 (seeFIG. 3).

It is to be noted that the eyelet 101 is provided with a recess 103located in a rectangular region that includes the periphery of the leadpin 123, so that the end surface 123 a of the lead pin 123 does notprotrude from the surface 101 a of the eyelet 101.

FIG. 2 is a front view of the essential part of the semiconductor laserdevice, while FIG. 3 is a top view of the essential part of thesemiconductor laser device shown in FIG. 2. In FIG. 2 and FIG. 3, theeyelet is not shown in order to make the figure easy to see.

As shown in FIG. 2, the two semiconductor laser elements 131 and 132 aredie-bonded onto metal lines 181 and 182 (shown in FIG. 3) formed on thesub-mount 160 with a brazing material (not shown) made of an Au—Snalloy. The two semiconductor laser elements 131 and 132 are arranged onthe Si sub-mount 160 so that the optical axes of the emission lightbecome parallel to each other and perpendicular to the surface of theeyelet 101. It is to be noted that the semiconductor laser element 131has a parallelogram-like section shape and is grown in a crystal form onan off-substrate.

The heat radiation base 102 is provided with stepped portions 111,besides a surface 102 a to which the Si sub-mount 160 is die-bonded. Thestepped portions 111 are located on both sides of the heat radiationbase 102 and have the surfaces 102 b that are parallel to the surface102 a and of varying heights. By virtue of the difference in heightbetween the surface 102 a and the surface 102 b, a silver paste 170coated on the surface 102 a does not spread outwardly of the edge of thesurface 102 a due to surface tension. As a result, the surface 102 b canmaintain smoothness and allows the metal wires 152 and 154 to be easilydie-bonded even after the Si sub-mount 160 is die-bonded to the heatradiation base 102. The heat radiation base 102 formed integrally withthe eyelet 101 (shown in FIG. 1) is electrically connected to the leadpin 124 (shown in FIG. 1) that serves as a common electrode.

The columnar lead pins 121 through 124 are made of metal, however, theirsurfaces are smoothly finished. Therefore, a contact surface parallel tothe upper electrode of the semiconductor laser element 132 exists on theouter peripheral surface of the lead pin 122 and therefore, they areable to be connected with a metal wire 153 by a conventional wirebonding apparatus. Likewise, a metal line 181 (shown in FIG. 3) formedon the Si sub-mount 160 and the lead pin 121 can be connected with ametal wire 151.

As shown in FIG. 3, a cathode 184 of the monitoring PD 140 is connectedto the cathode of the semiconductor laser element 132 via a metal wire156. On the other hand, an anode electrode 183 of the monitoring PD 140is connected to the end surface 123 a of the lead pin 123 via a metalwire 155. The end surface 123 a of the lead pin 123 is aboutperpendicular to the surface of the anode electrode 183 of themonitoring PD 140. Thus connecting together the bonding surfaces thatare about perpendicular to each other by way of one metal wire (90°wire) obviates the need for providing a monitoring PD independently ofthe Si sub-mount. There is no need for exposing the lead pin 123 byproviding the eyelet 101 of the stem 100 with a recess 103 (shown inFIG. 1). In other words, it is possible to remove the recess 103.Therefore, the semiconductor components such as the semiconductor laserelements and the monitoring PD can be protected by keeping airtight theinside of the semiconductor laser device with a cap. It is possible tohouse all the above-mentioned components in a compact package having anouter diameter of 5.6 mm.

FIG. 4 through FIG. 11 show the wire bonding processes of theaforementioned semiconductor laser device, and the wire bonding methodof the aforementioned semiconductor laser device will be described belowwith reference to FIG. 4 through FIG. 11. The wire bonding apparatus tobe used for the wire bonding method of this semiconductor laser devicehas the same construction as that of the wire bonding apparatus shown inFIG. 13 except for the arrangement that the angle of turn of the stem is90°, and the same components will be denoted by the same referencenumerals with no description provided for the components.

First of all, it is assumed that a first bonding surface is the surfaceof the anode electrode 183 (shown in FIG. 3) connected to the anode ofthe monitoring PD 140 (FIG. 1). It is assumed that a second bondingsurface is the end surface 123 a of the lead pin 123, and the endsurface 123 a is made so as not to protrude above the surface 101 a ofthe eyelet 101. This arrangement is adopted to prevent the capillary 71from colliding against the semiconductor laser elements 131 and 132 onthe Si sub-mount 160 by placing the capillary 71 as close to the surface101 a of the eyelet 101 as possible.

A distance from the center axis of the capillary 71 to the end surface123 a of the lead pin 123, or the second bonding surface is assumed tobe h1. The stem 100 is thus retained so that the axis of the capillary71 becomes perpendicular to the first bonding surface (anode electrode183) of the monitoring PD 140.

Next, the bonding head 70 is moved down as shown in FIG. 5, forming afirst bond X.

Next, the bonding head 70 is moved up as shown in FIG. 6. In this stage,a distance from the tip of the capillary 71 to the first bond X isassumed to be d2. This distance d2 should preferably be made longer thana distance d1 from the front end surface of the semiconductor laserelements 131 and 132 to the first bond X (d2>d1). With this arrangement,the capillary 71 can be prevented from striking against thesemiconductor laser elements 131 and 132 when the stem 100 is turned.

Next, as shown in FIG. 7, the stem 100 is turned around an axis O thatis located on the metal wire 50 extended between the first bond X andthe capillary 71, passes through a point of a specified height h2 fromthe first bond X and is perpendicular to the plane of the sheet of FIG.7. The “direction perpendicular to the plane of the sheet” is identicalto a direction in which the wire bonding is observed. That is, the axisO around which the stem 100 is turned is made parallel to a line ofintersection of the first and second bonding surfaces (anode electrode183 and end surface 123 a) that are approximately perpendicular to eachother.

By the above operation, as shown in FIG. 8, the distance from the tip ofthe capillary 71 to the first bond X and the distance from the tip ofthe capillary 71 to the second bond Y do not substantially change beforeand after the turn of the stem 100. Therefore, the metal wire 50 is notdrawn out of the capillary 71 while the stem 100 is turning, and thereis no concern about the disconnection of the metal wire 50.

More preferably, the height h2 of the axis O of the center of turn ofthe stem 100 in FIG. 7 is made equal to the height h1 in FIG. 4 (h2=h1).Then, the height d2 from the tip of the capillary 71 to the first bond Xshown in FIG. 6 becomes equal to a height d3 from the tip of thecapillary 71 to a second bond Y shown in FIG. 8 (d2=d3) before and afterthe turn of the stem 100, and the state of adhesion of the metal wire 50can be put in the best state.

Next, as shown in FIG. 9, the bonding head 70 is horizontally movedalong the end surface 123 a of the lead pin 123 after the stem 100 isturned by an angle of 90°, so that the tip of the capillary 71 islocated on a vertical line extending through the second bond Y of theend surface 123 a.

Then, the bonding head 70 is moved down again as shown in FIG. 10,performing bonding to the end surface 123 a of the lead pin 123 that isthe second bonding surface. The end surface 123 a of this lead pin 123is at most about 1 mm lower than the surface 101 a of the eyelet 101 ofthe stem 100, thereby permitting movement of capillary 71.

Finally, the wire clamp 73 is closed as shown in FIG. 11, and thebonding head 70 is moved up in the state, cutting the metal wire 50 forthe completion of the wire bonding.

The Si sub-mount formed integrally with the monitoring PD 140 will bedescribed next. As is well known, the semiconductor laser element emitslaser light not only from the front end surface but also from the rearend surface. This laser light emitted from the rear end surface of thesemiconductor laser element is partially incident on the monitoring PD140 formed integrally with the Si sub-mount 160, and a monitor outputfrom this monitoring PD 140 is used as a semiconductor laser opticaloutput control signal.

In the semiconductor laser device of this embodiment, the semiconductorlaser element 132 is of the AlGaAs system in which infrared laser lighthaving a wavelength of 770 nm to 850 nm is emitted and the lightemitting point is located approximately 50 μm apart from the surface ofthe Si sub-mount 160. On the other hand, the semiconductor laser element131 is of the InGaAlP system in which red laser light having awavelength of 630 nm to 680 nm is emitted and the light emitting pointis located approximately 5 μm apart from the surface of the Si sub-mount160.

If a height from the light emitting point of the semiconductor laserelement 131 to the surface of the Si sub-mount 160 has a small value ofapproximately 5 μm, then it is preferable to place the monitoring PD 140as close to the rear end surface of the semiconductor laser element 131as possible since the monitor signal is increased. However, if the metalline 181 mounted with the semiconductor laser element 131 is protrudingeven a bit from the rear end surface of the semiconductor laser element131 to the monitoring PD 140 side, then the emission light of thesemiconductor laser is reflected on the metal line, and the monitorsignal is reduced in magnitude to a fraction. As a result, the magnitudeof the monitor signal of the infrared laser light and the magnitude ofthe monitor signal of the red laser light significantly differ from eachother, and this requires a complicated control circuit. Therefore,according to the semiconductor laser device of this embodiment, themetal line 181 on the Si sub-mount 160 is made to have a pattern thatdoes not protrude on the monitoring PD 140 side in the vicinity of therear end surface 181 a (shown in FIG. 3) of the semiconductor laserelement 131.

Although the metal lines 181 and 182 formed on the Si sub-mount 160 alsoplay the role of heat radiation plates for the semiconductor laserelement 131 and 132, there is no problem even if the heat radiationbecomes worse since the rear end surface of the semiconductor laserelement generates heat less than that of the front end surface. Inparticular, the reflectance of the front end surface is set consistentlylower than the reflectance of the rear end surface in the case of a highpower semiconductor laser element of which the heat radiation isimportant, and therefore, the generation of heat in the vicinity of therear end surface does not become as large as that of the front endsurface.

In the semiconductor laser device of this embodiment, the semiconductorlaser element 131 has its p-electrode side die-bonded to the metal line181, while the semiconductor laser element 132 has its n-electrode sidedie-bonded to the metal line 182. This arrangement is adopted becausethe red semiconductor laser element 131 has low reliability and it isdesired to place the light emitting point in a position as close to themetal line as possible. On the other hand, the infrared semiconductorlaser element 132 is more advantageous when the p-side having a highersurface resistance is used as the die bonding surface. There is also theproblem that the p-side, which is an epitaxial surface, has significantunevenness, leading to difficult wire bonding. The metal lines 181 and182 are electrically insulated in the above-mentioned semiconductorlaser device. Therefore, even with the above-mentioned arrangement, thetwo semiconductor laser elements 131 and 132 are arranged not seriallybut allowed to be arranged parallel depending on the way of connectionof the metal wires 151 through 154 as shown in FIG. 2.

As is apparent from the above, according to the semiconductor laserdevice of the present invention, the electrode surface of the monitoringPD and the wire bonding surface of the lead pin are made to be thesurfaces that are perpendicular to each other. As a result, there can beprovided a semiconductor laser device in which two semiconductor laserelements and the monitoring PD are mounted on a small-size stem (havinga diameter of, for example, 5.6 mm).

The bonding position of the first bonding surface and the bondingposition of the second bonding surface are located within the identicalplane about perpendicular to those of the first and second bondingsurfaces, and the stem is turned along the identical plane in the wirebonding stage. Therefore, the metal wire is not twisted and stress isnot applied to the semiconductor laser element and the monitoring PD towhich the metal wires are connected. Therefore, the reliability can beimproved.

By separately making the metal lines on the Si sub-mount on which thesemiconductor laser elements are mounted and electrically insulating themetal lines from each other, the electrical characteristics on thedie-bonding side of the two semiconductor laser elements may bedifferent from each other. In other words, it is also possible todie-bond the p-electrode side of one semiconductor laser element anddie-bond the n-electrode side of the other semiconductor laser element.Therefore, the degree of freedom in using the semiconductor laserelements is improved.

In order to make a greater amount of emission light from thesemiconductor laser elements incident on the monitoring PD formedintegrally with the surface of the Si sub-mount, the metal lines on theSi sub-mount are formed so that the vicinities of the light emitting endsurfaces of the semiconductor laser elements do not protrude from thesemiconductor laser elements. This arrangement is effective particularlyfor a semiconductor laser element whose light emitting point is locatedseveral micrometers higher than the surface the Si sub-mount.

The end surface of the lead pin that serves as the second bondingsurface is located at the same height as that of the surface of the stemor lower than the surface of the stem. Therefore, the capillary of thewire bonding apparatus can be prevented from striking against the leadpin that has the second bonding surface when performing wire bondingonto the first bonding surface.

By providing the stem with the stepped portions that are parallel toeach other and have a difference in level between the surface to whichthe Si sub-mount is to be die-bonded and the stem surface to besubjected to wire bonding, the conductive paste is prevented fromadhering to the wire bonding surface. This eliminates the possibility ofthe occurrence of the problem that the metal wire does not adhere to thebonding surface.

According to the semiconductor laser device wire bonding method of thepresent invention, the metal wire can be connected to the first andsecond bonding surfaces that are about perpendicular to each otherwithout twisting the metal wire by connecting the metal wire to thefirst bond and thereafter turning the stem around the axis that extendsthrough the drawn metal wire and is perpendicular to the metal wire.

By setting the axis around which the stem is turned in the directionperpendicular to a plane on which the wire bonding is to be observed,the wire bonding can be performed while observing how the metal wire istwisted. Therefore, no failure of bonding occurs.

By setting the bonding position of the first bonding surface and thebonding position of the second bonding surface in an about identicalplane, the metal wires are not twisted and no stress is applied to thesemiconductor laser elements and the monitoring PD to which the metalwires are connected. Therefore, the reliability can be improved.

Furthermore, the distance from the axis around which the stem is turnedto the first bonding surface is set equal to the distance from the axisaround which the stem is turned to the second bonding surface. With thisarrangement, the distance from the tip of the capillary of the wirebonding apparatus to the first bonding surface and the distance from thetip of the capillary to the second bonding surface become equal to eachother before and after the turn of the stem. Therefore, the wire bondingcan easily be performed, and the bonded metal wires can be made hard tocome off.

By setting the length of the metal wire to be drawn from the position ofthe first bonding surface longer than the length from the front endsurface of the semiconductor laser element to the first die-bondingposition, the capillary can be prevented from striking against thesemiconductor laser element when the stem is turned in order to performwire bonding to the next second bonding surface.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A semiconductor laser device comprising: a stemprovided with a plurality of lead pins; a sub-mount that is die-bondedonto the stem and has a surface formed integrally with a monitoringphotodiode; and two semiconductor laser elements that are die-bondedonto the sub-mount and have emission light monitored by the monitoringphotodiode, the semiconductor laser elements having electrodeselectrically connected to the respective lead pins via metal wires andthe monitoring photodiode having an electrode electrically connected tothe corresponding lead pin via a metal wire, wherein at least one firstbonding surface of the two semiconductor laser elements and themonitoring photodiode is approximately perpendicular to a second bondingsurface of the lead pin to be wire-bonded to the first bonding surface.2. A semiconductor laser device as claimed in claim 1, wherein a bondingposition of the first bonding surface and a bonding position of thesecond bonding surface are located in an identical plane approximatelyperpendicular to the first and second bonding surfaces.
 3. Asemiconductor laser device as claimed in claim 1, further comprising:metal lines, which are formed on the sub-mount and to which the twosemiconductor laser elements are respectively die-bonded, wherein themetal lines corresponding to the semiconductor laser elements areelectrically insulated from each other.
 4. A semiconductor laser deviceas claimed in claim 1, further comprising: metal lines, which are formedon the sub-mount and to which the two semiconductor laser elements aredie-bonded, wherein no metal line is formed from a rear end surface ofat least one of the two semiconductor laser elements toward themonitoring photodiode.
 5. A semiconductor laser device as claimed inclaim 1, wherein an end surface of the lead pin is the second bondingsurface, and the end surface of the lead pin is located at a heightequal to a height of the surface of the stem or lower than the height ofthe surface of the stem.
 6. A semiconductor laser device as claimed inclaim 1, wherein the stem is provided with stepped portions havingbonding surfaces that are parallel to and different in height from asurface to which the sub-mount is bonded.
 7. A semiconductor laserdevice comprising: a stem provided with a plurality of lead pins; asub-mount die-bonded onto the stem; and a semiconductor laser elementdie-bonded onto the sub-mount, the semiconductor laser element having anelectrode electrically connected to the lead pin via a metal wire,wherein the stem is provided with stepped portions having bondingsurfaces that are parallel to and different in height from a surface towhich the sub-mount is bonded.